During an update of the ppm, I got an r/w error on my harddisk. ppm reported no space left on harddisk. Free space is > 25 GB. After restarting puppy the ppm didn't show the installed programs anymore. Normally on the uninstall tab listed, now the list is empty.

How is Slacko installed?
Full or frugal?
If frugal, how much free space in save file?_________________I have found, in trying to help people, that the things they do not tell you, are usually the clue to solving the problem.
When I was a kid I wanted to be older.... This is not what I expected

To see it in Rox file manager, you need to click on the eye icon, so hidden files are shown. The .packages directory is hidden.

You can click on this "user-installed-packages" file to open it and see what it contains.

What happens when you do that?_________________I have found, in trying to help people, that the things they do not tell you, are usually the clue to solving the problem.
When I was a kid I wanted to be older.... This is not what I expected

On the right side of the task bar is a personal storage icon.
When you hover over it, what does it say for free space?_________________I have found, in trying to help people, that the things they do not tell you, are usually the clue to solving the problem.
When I was a kid I wanted to be older.... This is not what I expected

With the "user-installed-packages" file being empty. I think you are out of luck.
That file only gets updates and entries by checking a file that is stored in the temp directory.
The contents of this temp directory get deleted on shutdown.

When you install a package the info is put in a temp file. The temp file is then checked to update the "user-installed-packages".

In /root/.packages there is a file for each package you have installed. This file is a list of what the package installed and where it installed.
I guess you could use this file to manually uninstall a package._________________I have found, in trying to help people, that the things they do not tell you, are usually the clue to solving the problem.
When I was a kid I wanted to be older.... This is not what I expected

During an update of the ppm, I got an r/w error on my harddisk. ppm reported no space left on harddisk.

Computers do stuff for no reason at any time.
Who knows why?
Storage space is not a problem.
All I can say is, stuff happens

If you try to update PPM and it still gives you this problem. You may have something wrong with the file system on the hard drive.

to check :
Run the program Gparted and have it do a check of the hard drive.

To use Gparted:
Boot with the Puppy live CD
At the Puppy boot screen hit F2 key.
Use the boot option puppy pfix=ram.
This keeps the hard drive from being mounted.
Hard drive can not be mounted for Gparted to work.

In Gparted
right click on a partition
Select check
If it finds anything wrong it will correct.

If you have more than one partition on hard drive
run a check on all of them._________________I have found, in trying to help people, that the things they do not tell you, are usually the clue to solving the problem.
When I was a kid I wanted to be older.... This is not what I expected

In /root/.packages there is a file for each package you have installed. This file is a list of what the package installed and where it installed. I guess you could use this file to manually uninstall a package.

So, in my understanding we have two files: one vanilla file "/root/.packages", should be available booting puppy in RAM-mode, and the live file in my installation. The difference between the two files are the packages, I installed. Am I correct?

The info file for a package you installed will be named for the program package you installed.
Example:
flashplayer 11

The other info files are all repository content info. They are used by PPM to show what is available from a specific repository of packages.
Example:
Packages-Puppy5-Official

In Rox file manager.
If you left click on a Puppy version sfs file it will open showing all contents of the Puppy version before any changes.
It does need to be one you are not using at the time._________________I have found, in trying to help people, that the things they do not tell you, are usually the clue to solving the problem.
When I was a kid I wanted to be older.... This is not what I expected